Reactors for hydrogen reformation have been developed to generate hydrogen from various hydrocarbon sources, such as methane, liquefied petroleum gas, liquid motor fuels such a petrol, diesel or methanol/ethanol. This process is generally carried out in two steps. Initially, hydrocarbons and water are converted into hydrocarbon gas and carbon monoxide in an endothermic reaction. This step is also known as a steam reformation process and the reaction takes place at temperatures above 600° C. In a further reaction step, the shift reaction, the carbon monoxide generated in the reforming reaction is converted with water into hydrogen gas and carbon dioxide. This shift reaction occurs at temperatures below 350° C. and is an exothermic reaction.
Hydrogen reformation has also been tried in a membrane reactor design using a process to directly convert hydrocarbons. This process generated hydrogen by converting the hydrocarbon stream in a membrane reactor fitted with a nickel-containing catalyst. WO99/43610, for example, describes a membrane reactor design that contains a hydrogen permeable membrane and a Ni catalyst to generate hydrogen directly from a hydrocarbon (avoiding the carbon monoxide step) through cracking. The hydrocarbon stream is brought into contact with the catalyst at temperatures between 400 and 900° C. so that conversion of the gas takes place, forming hydrogen. Subsequently, the hydrogen selectively permeates the membrane wall and leaves the reactor.
Hydrogen diffusion membranes often are made from palladium-based spiral or a spiral-shaped tube or tube bundle. Alternatively, a palladium alloy on a porous ceramic substrate can function as a hydrogen membrane. The catalyst bed generally consists of a granular bed of catalyst particles or a porous ceramic catalyst material coated with the catalyst. The catalyst bed and the hydrogen diffusion membrane are located in the same reactor vessel and the catalyst bed is often concentrically and coaxially arranged around the hydrogen diffusion membrane.
Reaction control in membrane reactors often requires supply of process heat into the reactor in order to carry out an endothermal reaction, such as the dehydrogenation of an alkane thiol into its corresponding thiophene.
Catalysts for chemical reactions are generally metals or metal oxides and often made from mixtures of metals called “alloys.” However, it is difficult to coat metal surfaces onto fibrous bases because of poor adherence and the fact that fibers bend while the metal surface layer does not. This causes flaking off of the metal surface layer and providing exposure of the fiber surface to the chemical milieu or even exposure of a sublayer or “glue-like layer to the chemical milieu where the reaction to be catalyzed is supposed to take place. The result is exposure of the chemical reactants to a mixed surface of desired catalyst, and undesired fiber surface and sublayer surface. The result of exposure to this mixed surface is wrongly catalyzed side reactions or inefficient reactions due to lower surface area of needed catalytic surface. Therefore, there is a need in the art to be able to provide relative continuous catalytic surfaces of the desired metal without exposure to sublayers or underlying fiber surfaces.
Metal coating of carbon fibers and gold in particular has been tried. For example, U.S. Pat. No. 4,606,354 describes a medical implant of a carbon fiber rod having a discontinuous coating for delivering gold ions to the site or an arthritic joint. Specifically this discontinuous gold fiber implant was made with nickel-coated carbon fibers because the group was unable to provide even a discontinuous coating on carbon fibers without a sublayer of another metal. Therefore, a discontinuous gold coating having a significant nickel surface would cause Ni-catalyzed reactions in addition to Au-catalyzed reactions and this resulting surface would be undesirable for a reactor module where side reactions (such as those catalyzed by Ni or a desulfurization nature) would be undesirable.
U.S. Pat. No. 4,816,124 describes metal coating a series of fibers (including carbon fibers) with metals, including gold. However, the metal coated fibers are for shielding and are not designed to operate at temperatures of reactor modules (such as above 200° C.) because the process requires the initial application of base coating resins in order to apply the metals and the base coating resins applied would not be able to operate at the elevated temperatures of a catalytic reactor module.
Catalytic surfaces must be made such that the catalyst does not get poisoned and to keep the reaction being catalyzed from forming unwanted side reactions. In the case of an alkane thiol, for example, much catalytic work has been done to try to desulfurize the molecule into a linear alkane or even a partially dehydrogenated alkene. Earlier characterization (Ratner and Naeemi, U.S. Pat. No. 7,186,396 (the disclosure of which is incorporated by reference herein) describe a gold catalyzed thiol that forms a thiophene and the release of three moles of hydrogen per mole of alkane thiol. Yet that reaction was conducted in a static or laboratory setting, not in a flow-through or dynamic environment. Therefore, there is a need in the art to design and build reaction modules capable of dehydrogenating an alkane thiol into a thiophene without side reactions of other desulfurized alkanes or alkenes. The present invention was made to design an appropriate catalytic surface to address this need.